The present invention relates to a degasifying valve for storage and/or transport containers, especially for the storage and/or transportation of dangerous liquids, comprising a base provided with a degasifying orifice, the downstream mouth of said orifice being surrounded by a valve seat, and a spring element being biased into sealing contact with said valve seat.
Such a degasifying valve may be arranged in the wall of the container as well as in the cover of the container.
In the chemical sector dangerous liquids must be stored or transported, respectively, which split off more or less gaseous materials which might set under pressure the container, if no precautions have been made for gas-escape. Gas-escape is made possible by degasifying valves which must be able to prevent the at least partially dangerous liquids from escaping together with the gaseous materials.
At present mushroom-shaped degasifying valves made of silicon rubber are used. These valves are provided with a shaft which is pressed into a degasifying orifice of the cover of the container, a ring-shaped swelling of the shaft abutting on the inner surface of the top plate of the cover, whereas the rim of the convex valve head is abuting on the outer surface of said top plate by influence of a biasing force which depends on the thickness of the top plate and the distance between valve head and ring-shaped swelling. The ring-shaped swelling is provided with a groove extending in the direction of gas flow through the orifice and allowing the escape of the gas when the pressure of the gas lifts off the rim of the valve head from the outer surface of the top plate of the cover. When gas escapes gas pressure descends and the rim of the valve head will again abut on the outer surface of the top plate.
In many cases this mushroom-shaped valve is arranged in a plastic housing and is mounted in the top plate of the cover together with this housing. The function is the same as described above.
Years ago thin circular metal plates were inserted into the top plate of the cover which were split radially so that the plates would bend by the influence of gas pressure thereby opening slots allowing the escape of the gas. However, escape of the dangerous liquid cannot be fully avoided by this very construction.
But also the above mentioned mushroom-shaped valve is not able to meet strict security requirements. Nearly all of the elastic and flexible plastic materials which may be used for this valve construction are not resistent when coming into contact with most of the dangerous liquids. In some cases the valve bodies swell, so that at least the spring characteristic changes and as a result the biasing force and the opening pressure, whereas in cases of extreme swelling the function of the valve will be seriously disturbed and even blocked. As a further result the pressure in the container may increase to such an extent that the container may be destroyed. In other cases the valves are totally destroyed when moistened by aggressive liquids thus allowing the escape of dangerous liquids.